You can never have enough button design inspirations, this set of design comes from David Conner. There are five designs to choose from, the first one is a ghost style button which on hover transforms the button border to an underscore. The next effect adds a line above and below the button text on hover. The third effect has a 3D touch to it giving the impression of a pushed down button on hover. The fourth button gives a shine effect that slides from the top left to the bottom right on hover. The final button sends out a small pulse like effect from the button border.
If you are having trouble with the pen, try the archived copy on GitHub